1. Field of the Invention
The present invention generally relates to monolithic ceramic capacitors and structures for mounting the same and, more particularly, to an improvement that achieves both size reduction and improved moisture-resistance reliability of monolithic ceramic capacitors.
2. Description of the Related Art
Reliability under a high-temperature high-humidity loaded environment, that is, moisture-resistance reliability, is one of important required characteristics of monolithic ceramic capacitors. Decreased moisture-resistance reliability is more likely to cause a decrease in insulation resistance of monolithic ceramic capacitors under a high-temperature high-humidity loaded environment.
Hitherto, various improvements have been attempted in order to improve moisture-resistance reliability of monolithic ceramic capacitors. Many of such improvements are directed toward material compositions of a conductive paste used to form outer electrodes and structures of the outer electrodes. A presumable reason for this is as follows. Moisture often intrudes into a multilayer body which is a main body of monolithic ceramic capacitors from surfaces of the multilayer body having lead portions of inner electrodes disposed thereon. It has been considered that blocking moisture intrusion with outer electrodes that are formed to cover the lead portions of the inner electrodes is the most effective way to prevent such moisture intrusion.
For example, Japanese Unexamined Patent Application Publication Nos, 2000-40635, 2000-49034, and 2000-77258 describe a material composition of a conductive paste used to form outer electrodes or a structure of the outer electrodes that is effective to improve moisture-resistance reliability.
More specifically, Japanese Unexamined Patent Application Publication No. 2000-40635 describes a material composition used to form outer electrodes. This material composition allows reaction layers which have a certain thickness and can contribute to improvement in moisture-resistance reliability to be formed between dielectric ceramic layers included in a multilayer body and the respective outer electrodes.
Japanese Unexamined Patent Application Publication No. 2000-49034 focuses on porosity rates of outer electrodes in order to improve moisture-resistance reliability and describes particle diameters of metal powder contained in conductive pastes and a multilayer structure of the outer electrodes for achieving desired porosity rates.
Japanese Unexamined Patent Application Publication No. 2000-77258 describes an average particle diameter of metal particles and a glass distribution area ratio at surfaces of outer electrodes for improving moisture-resistance reliability.
There is also a desire for smaller monolithic ceramic capacitors in order to implement high-density packaging while maintaining an electrostatic capacity thereof. To meet such a desire, for example, reducing a thickness of outer electrodes is effective. Reducing a thickness of outer electrodes, and thereby reducing the material cost of the outer electrodes can also contribute to a reduction in the overall cost of monolithic ceramic capacitors.
However, it is easily presumed that a reduced thickness of outer electrodes, which have a role for blocking moisture intrusion into a multilayer body as described before, leads to the decreased moisture-resistance reliability.